In the formation of an x-ray image (hereinafter also referred to as an image) of an object which is a predetermined part (for example, the breast part or abdominal part of a human body with a motion), there are a plurality of x-ray imaging condition combinations (hereinafter also referred to as imaging condition combinations) which provide equivalent analog photograph concentrations (hereinafter also referred to as equivalent concentrations) or equivalent digital exposure index (EI) values (hereinafter also referred to as equivalent EI values). Each of the plurality of imaging condition combinations includes, for example, the distance between an x-ray tube focal plane and an x-ray detector system plane, the distance between the x-ray tube focal plane and an object plane, an x-ray tube nominal focal spot value, a tube voltage, a tube current, imaging time, and the kind of an x-ray detector system.
When imaging an object of a human body with a motion, it is difficult to predict an imaging condition combination which enables obtainment of a high-resolution Image in a short period of time.
Currently, as an example of a method for predicting an imaging condition combination which enables obtainment of a high-resolution image, there is a method for imaging test charts with a motion under different imaging condition combinations, and comparing the resolutions of the resulting images by means of visual check. However, this method requires extremely long time to perform tests on all of the imaging condition combinations. In addition, since the resolutions are compared by means of visual check by humans, there are cases where the resolutions are not compared accurately.
As another example of a method for predicting an imaging condition combination which enables obtainment of a high-resolution image, there is a method for comparing resolution characteristics (MTFs). This method focuses on total MTFs each generated based on three major elements which blur an image. The total MTF is an MTF obtained by multiplying an MTF based on an x-ray tube effective focal spot value, an MTF based on the amount of motion of the object, and an MTF based on the kind of the x-ray detector system.
Non-patent Literatures 1 to 4 disclose techniques related to such MTFs.
More specifically, Non-patent Literatures 1 to 4 disclose examples of approximate functions of MTFs based on the kinds of x-ray detector systems as blurring elements. Non-patent Literatures 1 to 4 further disclose examples of approximate functions of MTFs based on the amount of motion of objects as blurring elements. Non-patent Literatures 1 to 4 further disclose examples of approximate functions of MTFs based on x-ray tube nominal focal spot values as blurring elements. Furthermore, Non-patent Literatures 1 to 4 disclose that approximate functions of total MTFs are generated by multiplying approximate functions of MTFs based on x-ray tube nominal focal spot values and approximate functions of MTFs based on the kind of the x-ray detector systems, and that simulation is performed based on approximate functions of the total MTFs. In this way, the approximate functions of the total MTFs are generated for respective imaging condition combinations through a fast operation process by a computer or the like in a short period of time. By means of the approximate functions of the total MTFs are generated for the respective imaging condition combinations being expressed using numerical values or a graph, it is possible to compare the differences in resolution characteristics due to the differences in the imaging condition combinations.